Final klystron modulator design, testing, and installation plan for the Los Alamos Neutron Science Center accelerator

This paper describes the production design, initial testing, and the installation plan of the 44 totem-pole pair, triode based klystron modulator systems that will be installed on the Los Alamos Neutron Science Center (LANSCE) accelerator RF system. The existing modulators were designed in the late 60's and replacement components are no longer available. That design uses a single triode tube as a saturated switch to develop the required klystron mod-anode voltage. This design dissipates almost 15 kW and requires oil pumps and oil/water heat exchangers to maintain safe oil tank temperatures. The new modulator switches electrostatically, charging and discharging the klystron mod-anode capacitance. Analog feedback control is utilized to ensure the klystron beam current is flat-top regulated. The new totem-pole design also provides faster rise and fall characteristics which reduces klystron collector dissipation. The new modulator is designed to operate the klystrons up to 86 kV with a nominal 32 Amp beam current at a 120 Hz repetition rate and a 15% duty cycle (>400 kW). The on and off deck modulators are of identical design and utilize a cascode connected planar triode, cathode driven with a high speed MOSFET. Voltage divider feedback is connected to the planar triode grid to enable flat-top control. Although modern design approaches suggest solid state designs may be considered, the planar triode (Eimac Y-847B) is very cost effective and has a low power (50 W) matrix cathode which is easy to integrate with the existing hardware. With the high mu gain characteristics, the triode provides a simplified linear feedback control mechanism. The design is very compact and fault tolerant. This paper will review the final design, test parameters, and the expected installation plan for the LANSCE accelerator.